Bearing Fatigue Tests Research Articles

Damage Propagation by Cyclic Loading in Drilled Carbon/Epoxy Plates

Fiber reinforced composites are widely used in the production of parts for load bearing structures. It is generally recognized that composites can be affected both by monotonic and cyclic loading. For assembly purposes, drilling is needed, but holes can act as stress concentration notches, leading to damage propagation and failure. In this work, a batch of carbon/epoxy plates is drilled by different drill geometries, while thrust force is monitored and the hole's surrounding region is inspected. Based on radiographic images, the area and other features of the damaged region are computed for damage assessment. Finally, the specimens are subjected to Bearing Fatigue tests. Cyclic loading causes ovality of the holes and the loss of nearly 10% of the bearing net strength. These results can help to establish an association between the damaged region and the material's fatigue resistance, as larger damage extension and deformation by cyclic stress contribute to the loss of load carrying capacity of parts.

Rolling contact fatigue crack propagation on contact surface and subsurface in mixed mode I+II+III fracture

Rolling contact fatigue (RCF) is the critical damage from rolling bearings constraining the service, performance, and reliability, which is directly caused by fatigue crack propagation. The crack paths on both the contact surface and subsurface were observed after the bearing fatigue test. The three-dimensional geometry of the RCF crack was characterized and reconstructed based on experimental statistics. Finite element analysis was performed to obtain the mixed mode stress intensity factors (SIFs) along the crack fronts, and the crack propagation behavior was numerically studied. Results indicated that the propagation of cracks on the contact surface and subsurface causes the gradual formation of micropits and the sudden spalling of material respectively. Initial micro-cracks with an inclination angle of 15–30° have the highest growth rate, which should be prevented during the bearing raceway manufacturing process. The propagation paths of the RCF cracks can be more accurately predicted by considering the superposition of fracture mode I + II + III in three-dimensional, and mechanisms of crack propagation on contact surface and subsurface were revealed respectively.

Dynamic Analysis of Outer and Inner Race Defects on Thermoplastic Rolling Bearing System Using Implicit Finite Element Method

This paper proposes an improved finite element dynamic model to analyze the vibration response of a rolling bearing system. The vibration responses of defect free and defective polypropylene (PP) bearings are analyzed using the finite element analysis and compared with the experimental results using the in house developed bearing fatigue test rig. The boundary conditions of this model are imposed to ensure an adequate homogeneity with the experimental apparatus. This study considers the viscoelastic property of thermoplastic to investigate the effect of the flexibility and damping viscosity of material. The three-dimensional dynamic analysis detects the vibrations produced in a rolling bearing system. Modal frequencies and the vibration modes shapes which must be avoided had been determined. Monitoring the evolution of vibration signatures as a function of defect location is also carried out using Finite Element Analysis (FEM). Test results reveal that peak vibration amplitudes are more pronounced in an inner ring defect than in an outer ring defect. Vibration signals of stainless-steel bearings are investigated to compare the performance of the thermoplastic bearings with its metallic counterparts. Both test and simulation results reveal that a lower level of vibration is observed with PP bearings compared to that of metal. The PP bearings not only dampen vibrations, but also accommodate shaft misalignments unlike their steel counterparts. Once overall vibration spectrums results are validated, Von Mises stresses within the rings are evaluated under excessive loading conditions. The simulation results show that stress is high in raceways where the balls are compressed between the raceways. Computational results agree well with the experimental tests for the test scenarios.

Analysis and Experimental Validation of the Tribological and Dynamic Characteristics of Journal Bearings

Sliding bearings are the main kinematic pair of a Stirling engine, and one of the main sources of friction power loss and excitation force. There is a coupling effect between the lubrication state and the excitation force. In this paper, the dynamic model of a Sapphire bearing fatigue test bed, which includes thermo-elasto-hydrodynamic (EHD) property, is established and the accuracy of the model is verified by the experimental data. Based on the model, the effects of the load, the oil supply temperature, the oil supply pressure, the bearing clearance on the tribological and dynamic characteristics are studied. With an increase in the load, the orbital path of the journal moves downward, the lubrication state changes from the full hydrodynamic lubrication to the boundary lubrication, the friction power loss increases, and the bearing excitation frequency increases. Due to the decrease of the oil viscosity, the hydraulic friction power loss decreases, but the friction power loss derived from the asperity contact increase, so does the total friction power loss. With the increase of the radial clearance, the shape of the orbital path and the minimum oil film thickness remain unchanged. The increase of the bearing clearance results in the collisions between the journal and bearing bush, thus the amplitude of the frequency multiplication component in the bearing load increases, and the asperity and the total friction power loss increase.

Early Detection and Identification of Fatigue Damage in Thrust Ball Bearings by an Acoustic Emission Technique

As rolling bearings are widely used in various machines, there is a strong need to detect any problems as early as possible. Although vibration analysis is commonly used in the diagnosis of rolling bearings, it is possible that the failure of such bearings might be detected earlier by an acoustic emission (AE) technique. Methods for detecting potential fatigue damage in a thrust ball bearing by AE signal analysis and by vibration analysis were compared. For the AE signal analysis, the maximum amplitude and the frequency spectrum were used to detect and identify fatigue damage in the bearing. Features of AE signals detected when a defect was artificially formed on the raceway surface of a bearing by using a Vickers hardness tester were also examined. The AE technique detected initial cracks due to fatigue damage earlier than the vibration technique. Additionally, AE signals were always detected during bearing fatigue tests, but the AE signals detected during the running-in process, crack initiation, crack propagation, and flaking all contained different frequency components. Furthermore, the correlation map between the frequency spectra of AE signals and deformation and fracture phenomena (friction and wear modes) was updated by adding the new findings of this study.

Simulation and experimental verification of fatigue strength evaluation of journal bearing bush

The fatigue strength of journal bearing exampled with tin-based Babbitt bushes was calculated with fluid-structure interaction technique. The oil film pressure obtained by considering the cavitation in fluid simulation was loaded on the inner surface of bearing alloy as a boundary condition of fatigue analysis. The tests for the S-N curve of tin-based alloy were carried out in the hydraulic servo dynamic fatigue testing machine. To verify the simulation results, the bearing fatigue tests were conducted on the sapphire bearing bush fatigue testing machine with the same geometry, materials and boundary conditions as in the simulation. Results from simulation and experiment are quite consistent with each other.

Study on the ultimate load carrying capacity of journal bearings with different materials and surface treating processes

The ultimate load carrying capacity of journal bearings with different materials and surface treatment processes was studied in the present work. The load carrying capacity and backside temperature of bearing were examined using a bearing fatigue test machine (Glacier Vandervel, made in UK). The results showed that the copper-based sputtering bearing has the highest ultimate bearing capacity and the fatigue strength reaches 131.3 MPa. The bearing capacity of copper-based electroplated bearings is 99.7 MPa, which is lower than that of copper-based sputtering bearings. The bearing capacity of high tin aluminum alloy is obviously higher than that of white alloy bearing, and the bearing capacity of the two bearings is 72.7 MPa and 36.3 MPa, respectively. Finally, the mechanisms of fatigue failure of the bearings were analyzed.

Enhancement of roller bearing fatigue life by innovative production processes

Purpose The efficient and economical use of natural resources is a big issue. Machine elements with a rolling contact are highly relevant because of their wide application in technical systems and a large production quantity. Innovative hard machining can reduce the friction and increase the fatigue strength of rolling element bearings. The purpose of this study is to focus on the surface properties of such parts. Design/methodology/approach A new model to predict bearing fatigue life is presented which takes compressive residual stresses in the bearing subsurface area into consideration. The investigated bearings were machined by the processes of hard turning, hard turning with subsequent deep rolling and a combination of hard turning and deep rolling (turn-rolling) in one process step. Changes in the residual stress state during bearing fatigue tests were investigated and the influence of residual stresses on the bearings fatigue life was researched. Findings Both combinations including the deep rolling process decrease the surface roughness and induce compressive residual stresses. As a result, the L10 fatigue life of roller bearings was increased by the factor of 2.5. Owing to the developed models, this effect can be considered within the design process. Originality/value In the context of the research program “Resource efficient Machine Elements (SPP1551),” machining processes of bearings were investigated regarding the bearing fatigue life. By inducing beneficial residual stresses on the bearings’ subsurface area, the fatigue life could be increased. Thus higher resource efficiency was achieved. To increase the productivity, a combination of hard turning and deep rolling was evaluated.

Contact and wear thermo-elastohydrodynamic model validation for engine bearings

Tribological machine components such as engine crankshaft bearings operating at high load or rotational speeds often experience very thin oil films leading to asperity contact between the bearing and crankshaft. When the oil film thickness drops below the peak asperity height there is an increase in contact, wear and asperity power loss leading to worsening severity factors and seizure risk. Key factors influencing the bearing lubrication performance are the surface characteristics of the materials at the contact interface. SABRE-TEHL is a software simulation tool used for performing thermo-elastohydrodynamic analysis of bearing applications. In this current study, the development of a combined contact and wear model is demonstrated. This includes a hard contact model giving a direct surface contact pressure in areas of zero oil film thickness, a surface yield model with yield limits and plastic gradient from measured stress–strain data, an asperity wear model using measured surface roughness data and an asperity contact model based on measured roughness, asperity density and tip radius. Input surface roughness data are measured using a white light interferometry method. The effects of surface characterization in terms of roughness and stiffness properties are demonstrated using simulation results comparing an aluminium bimetal bearing with a polymer coated bearing, showing a significant reduction in asperity friction for the bearing with a polymer coating. Simulation results are compared with experimental test results for a 1.5 l diesel engine, a 2.0 l diesel engine and for a bearing fatigue test rig. Generally good agreement is seen when comparing the wear contours and wear depth on the bearing surface.

English

Bearing is an important component of a rotating machine; however, under normal operating conditions, it is subjected to fatigue which results in a defect called spalling. This work presents a monitoring fatigue of a thrust ball bearing on a bearing fatigue test bench. Spalling is artificially initiated on a bearing raceway. Vibration analysis is the method used to characterize the defect. The experimental procedure used is to monitor the operation of the ball bearing to the degradation with an online acquisition of the vibration readings. These data allow plotting the curve of fatigue (mathematical model). In order to obtain more realistic curve, the spalling evolution of several thrust ball bearings is monitored, first, under different loads then at different rotation speeds under a constant load. It found that growth follows a spalling power law and the damage is characterized by the model parameters.   Key words: Predictive maintenance, bearing, vibration analysis, spalling, rolling fatigue. &nbsp

Comparison of Black Oxide and Tungsten Carbide–Reinforced Diamond-Like Carbon (WC/a-C:H) Surface Treatments for Rolling Element Bearings

Surface-initiated damage increasingly limits the service life of rolling element bearings in challenging environments. In particular, operation in the boundary lubrication regime and/or conditions that produce excessive rolling element–raceway slip require the use of surface treatments on roller bodies and raceways to extend surface durability and component life. The tribological performance of two approaches is compared and contrasted: black oxide chemical conversion treatment and tungsten carbide–reinforced diamond-like carbon (WC/a-C:H) thin film hard coating. Black oxide treatment is performed on both rollers and raceways, whereas WC/a-C:H coatings are deposited on rollers only. The cross-sectional layer structure is compared using transmission electron microscopy, and mechanical properties are measured using nanoindentation. Ring-on-ring friction and wear testing is conducted to obtain Stribeck curves and evaluate adhesive wear resistance and cyclic acceleration performance. Tapered roller bearing fatigue test results are reported for treated bearings. Results from both bench-scale tribological tests and bearing fatigue tests indicate the superiority of WC/a-C:H coatings in protecting against severe adhesive wear damage and extending bearing fatigue life in boundary-lubricated conditions.

Assessment Method for Rolling Bearing Performance Degradation Using TESPAR and GMM

Rolling bearing performance degradation assessment has been receiving much attention for which itscrucial role to realize CBM(condition-based maintenance).This paper proposed a novel bearing performance degradation method based on TESPAR(Time Encoded Signal Processing and Recognition)and GMM(Gauss Mixture Model). TESPAR is used to extracted features which constitute A-matrix. GMM is utilized to approximate the density distribution of singular values decomposed by A-matrix. TENLLP(Time-Encoded Negative Log Likelihood Probability) serves as a fault severity which can display the similarity of the singular values between normal samples and fault samples as quantificational. Results of its application to bearing fatigue test show that this performance degradation assessment can detect the incipient rolling bearing fault and be sensitive to the change of fault.

Rolling Bearing Performance and Film Formation Behavior of Four Multiply Alkylated Cyclopentane (MAC) Base Greases for Space Applications

Four multiply alkylated cyclopentane (MAC)-based greases, used for space applications, were used for rolling contact fatigue tests employing thrust ball bearings. These greases were R2000, ML, MU, and 5200 and were made from the same base oil 2001A. Each grease had a different thickener, which were sodium soap, Li soap, urea, and polytetrafluoroethylene (PTFE), respectively. The effect of the grease thickener on the ball bearings' fatigue life in vacuum and atmospheric environments was investigated via testing. For the greases R2000, MU, and ML it was found that the oil film formation in the experiments performed under vacuum conditions declined remarkably in comparison to under atmospheric conditions. For the 5200 grease, the oil film formation was almost the same as under atmospheric conditions. These results were supported by the occurrence of cage wear in the ball bearing fatigue tests. In the absence of sufficient films, high wear rates were measured.

Bearing Fatigue Life Tests of Two Advanced Base Oils for Space Applications Under Vacuum and Atmospheric Environments

Four series of rolling-element bearing fatigue tests were conducted with 51104 size thrust ball bearings with three balls made from SUJ2 (AISI 52100) steel lubricated with two advanced synthetic base oils used for space applications. The test lubricants were perfluoropolyether (PFPE) and multiply alkyated cyclopentane (MAC). Each oil was tested with bearings under vacuum and atmospheric environments. The bearings were tested at a maximum Hertzian stress of 4 GPa on the inner and outer races. The outer race was rotated at a speed of 250 rpm. A pool lubrication system was used. Fresh lubricant was used for each test bearing. Testing in vacuum conditions was at 5 × 10−2 Pa. The test oils were analyzed to determine whether changes occurred as a result of operating in air and in a vacuum. In a vacuum environment, the PFPE 815Z oil exhibited a longer fatigue life than the MAC 2001A oil. However, in an air environment, the MAC 2001A oil had a longer L10 fatigue life than the PFPE 815Z oil. The fatigue life tests of PFPE 815Z oil in vacuum resulted in a longer L10 life than when tested in an air environment. In an air environment, hydrogen fluoride was generated in the bearing tests with the PFPE 815Z oils. Under vacuum conditions, hydrogen fluoride was not generated with the PFPE 815Z oil, resulting in longer bearing fatigue lives. The fatigue life tests of MAC 2001A oil in a vacuum resulted in shorter L10 fatigue life than in an air environment. The shorter life was attributed to the lower elastohydrodynamic oil film formation with the MAC 2001A oil because of a higher operating temperature and decomposition of the oil in vacuum.

A 3D Finite Element Study of Fatigue Life Dispersion in Rolling Line Contacts

Rolling contact fatigue of rolling element bearings is a statistical phenomenon that is strongly affected by the heterogeneous nature of the material microstructure. Heterogeneity in the microstructure is accompanied by randomly distributed weak points in the material that lead to scatter in the fatigue lives of an otherwise identical lot of rolling element bearings. Many life models for rolling contact fatigue are empirical and rely upon correlation with fatigue test data to characterize the dispersion of fatigue lives. Recently developed computational models of rolling contact fatigue bypass this requirement by explicitly considering the microstructure as a source of the variability. This work utilizes a similar approach but extends the analysis into a 3D framework. The bearing steel microstructure is modeled as randomly generated Voronoi tessellations wherein each cell represents a material grain and the boundaries between them constitute the weak planes in the material. Fatigue cracks initiate on the weak planes where oscillating shear stresses are the strongest. Finite element analysis is performed to determine the magnitude of the critical shear stress range and the depth where it occurs. These quantities exhibit random variation due to the microstructure topology which in turn results in scatter in the predicted fatigue lives. The model is used to assess the influence of (1) topological randomness in the microstructure, (2) heterogeneity in the distribution of material properties, and (3) the presence of inherent material flaws on relative fatigue lives. Neither topological randomness nor heterogeneous material properties alone account for the dispersion seen in actual bearing fatigue tests. However, a combination of both or the consideration of material flaws brings the model’s predictions within empirically observed bounds. Examination of the critical shear stress ranges with respect to the grain boundaries where they occur reveals the orientation of weak planes most prone to failure in a three-dimensional sense that was not possible with previous models.

Problems of Analytical Determination of Journal Bearing Bush Fatigue Strength Estimates

Problems connected with determination of stress distribution in sliding layer of thin-walled bearing bushes, investigated in bearing fatigue test rigs, have been presented. Using an example of plain bearings tested in the fatigue machine SMOK (built at the Gdańsk University of Technology) problems with obtaining a convergence of iterative procedure for determining the fatigue strength estimators of bearing alloy surface layer are analyzed. Calculations consisting in successive iterations of pressure distribution in oil film and corresponding elastic deformation of the bearing bush and housing were based on finite-element method and utilized ANSYS program. The objective of calculation was the estimation of values of radial, tangential, axial and reduced stresses in surface layer of the bearing bush corresponding to experimentally determined load magnitudes leading to fatigue cracks initiation. The convergence of analytical procedure has been achieved by the use of a relaxation method.

Fundamental Study on the Use of the Unisteel Bearing Tester to Differentiate Driveline Lubricant Additive Performance

The impact of driveline lubricants on rolling element bearing fatigue has been an important concern for many years. The recent emphasis on improved drivetrain efficiency has further heightened interest in the impact of lubricants on bearing life. A number of laboratory roller bearing test machines have been used to qualify lubricants for automotive applications. Included in these is the Unisteel Rolling Fatigue Testing Machine. We herein present results from an experimental matrix of driveline additives tested using a Unisteel test procedure. Statistical analysis of the cycles to pitting failure suggests that there was no difference in calculated bearing fatigue life between additive families taken as a group. Failure analysis of the end-of-test bearings suggests that the observed fatigue lives were primarily governed by poor surface finish on a flat test specimen commonly used to increase contact stress in accelerated Unisteel bearing fatigue test procedures.

Effects of extreme pressure additive chemistry on rolling element bearing surface durability

Lubricant additives have been known to affect rolling element bearing surface durability for many years. Tapered roller bearings were used in fatigue testing of lubricants formulated with gear oil type additive systems. These systems have sulfur- and phosphorus-containing compounds used for gear protection as well as bearing lubrication. Several variations of a commercially available base additive formulation were tested having modified sulfur components. The variations represent a range of “active” extreme pressure (EP) chemistries. The bearing fatigue test results were compared with respect to EP formulation and test conditions. Inner ring near-surface material in selected test bearings was evaluated on two scales: the micrometer scale using optical metallography and the nanometer scale using transmission electron microscopy (TEM). Focused-ion beam (FIB) techniques were used for TEM specimen preparation. Imaging and chemical analysis of the bearing samples revealed near-surface material and tribofilm characteristics. These results are discussed with respect to the relative fatigue lives.

Bolt bearing fatigue of polymer matrix composites at elevated temperature

Polymer matrix composites (PMCs) are being considered for a number of elevated temperature (177°C/350°F) aerospace applications. Mechanical fasteners may be required to join these PMCs, making the elevated fatigue behavior of these highly loaded joints a possible design concern. A modified test set-up was used to simulate the stress state of a bolted composite joint. Using this modified set-up, IM7/PETI-5 showed a 20% improvement over IM7/K3B in elevated temperature bearing fatigue tests. Furthermore, the bearing fatigue life of IM7/PETI-5 showed no dependence on frequency or 10,000 hours thermal aging. Upon completion of the fatigue testing, failure analysis revealed that the bearing failure mechanisms were delamination, ply buckling, and 0°-ply fracture. Overall, IM7/PETI-5 was found to be very durable with no significant time dependant behavior at 177°C (350°F).

The Effects of Fastener Hole Defects

The influence of drilling-induced defects, such as delamination, on the fa tigue life of a pin bearing joint in a toughened carbon epoxy system was investigated. In a pin bearing joint, the parameters of interest are the bearing stress and the pin position or tolerance. Tension bearing by-pass tests were conducted on coupons under ambient and elevated temperature wet conditions. Specimens were tested in a bearing tension frame to static failure in order to measure the failure load and to calculate pin bearing stress. From static test results, a fatigue load was selected as 66% of the static pin bearing failure load. Coupons were then tested under pin bearing fatigue loading at ambient and elevated tem perature wet conditions. Two-dimensional finite element models were used to simulate the pin and tension loads applied to the coupons. These models simulated the stress distribu tion around the loaded pin. The loads in the finite element models represented the failure load incurred in the static pin bearing tests as well as the maximum load during a selected cycle of the pin bearing fatigue tests. Experimental results showed the pin movement to vary with respect to delamination diameter, specimen thickness, and configuration. Numerical results compared with the static failure levels and indicated the form of the delaminated regions. Results give an indication of the effects of environment and hole quality under pin bearing load. Large variations in drilling-induced damage tended to cause variations in the pin bearing response of like specimens.